how to filter null values from map in Dart

Question

Following the map, having both key-value pair as dynamic, Write a logic to filter all the null values from Map without us?

Is there any other approach than traversin

Answer 1

I did this to make it easy remove nulls from map and list using removeWhere: https://dartpad.dartlang.org/52902870f633da8959a39353e96fac25

Sample:

final data = 
  {
    "name": "Carolina Ratliff",
    "company": null,
    "phone": "+1 (919) 488-2302",
    "tags": [
      "commodo",
      null,
      "dolore",
    ],
    "friends": [
      {
        "id": 0,
        "name": null,
        "favorite_fruits": [
          'apple', null, null, 'pear'
        ]
      },
      {
        "id": 1,
        "name": "Pearl Calhoun"
      },
    ],
  };

void main() {
  // From map
  print('Remove nulls from map:\n' + data.removeNulls().toString());
  // From list
  print('\nRemove nulls from list:\n' + [data].removeNulls().toString());
}

Answer 2

You can now use a map literal with conditional entries:

Map<String, dynamic> toMap() => {
  if (firstName != null) 'firstName': firstName,
  if (lastName != null) 'lastName': lastName,
};

Answer 3

I suggest you to use removeWhere function

    Map<String, dynamic> map = {
      '1': 'one',
      '2': null,
      '3': 'three'
    };

    map.removeWhere((key, value) => key == null || value == null);
    print(map);

Answer 4

Use removeWhere on Map to remove entries you want to filter out:

void main() {
  final map = {'text': null, 'body': 5, null: 'crap', 'number': 'ten'};

  map.removeWhere((key, value) => key == null || value == null);

  print(map); // {body: 5, number: ten}
}

And if you want to do it as part of your toMap() method you can do something like this with the cascade operator:

void main() {
  print(A(null, 'Jensen').toMap()); // {lastName: Jensen}
}

class A {
  final String firstName;
  final String lastName;

  A(this.firstName, this.lastName);

  Map<String, dynamic> toMap() {
    return <String, dynamic>{
      'firstName': this.firstName,
      'lastName': this.lastName
    }..removeWhere(
        (dynamic key, dynamic value) => key == null || value == null);
  }
}